38 MOLLUSCA. 
yellowish-green colour. Surface regularly marked with sharp, coarse 
lines of growth, which are crossed by fine, crowded, revolving lines, 
that merely cut the summits of the radiating lines, so that to the 
naked eye the surface appears minutely granulated, but under the 
lens the raised spaces are seen to be cut into squares. Whorls five, 
separated by a deep suture, the outer one proportionally large. Aper- 
ture nearly circular, a little angular at base, modified by the preceding 
whorl ; lip acute, simple. 
Diameter half an inch; axis eleven-fortieths of an inch. 
Inhabits Puget Sound, Oregon. Pzckering. 
Much like H. concava, Say, which, however, presents a very smooth 
surface, a smaller and less circular aperture, an umbilicus much 
broader, as the outer whorl increases less rapidly. I know of no 
North American species which has the surface similarly decussated. 
The specimens are immature, and probably the lip is sightly reflected 
or thickened in adults. 
Figures 42, 42 a, 42 b, three views of the shell ; 42 c, magnified por- 
tion of the surface. 
HELIx spPrRILuus (Gould). 
Testa parva, planorboidea, tenuis, diaphana, levis, virescens: spira de- 
pressa, anfractibus quinis convextusculis, arcté volutatis, ad periphe- 
riam rotundatis ; sutura impressa: apertura subcircularis ; labro 
albo, reflexiusculo ; columella callo subdentato munita. 
ANIMAL almost transparent, of a delicate straw-colour. [4. Pp. c.] 
SHELL small, depressed, slightly convex above, broadly concave 
beneath, thin, translucent, nearly smooth, of a greenish-drab (watery- 
green) colour. Spire composed of five slightly convex, closely revoly- 
ing whorls, separated by a deep suture; periphery rounded beneath, 
with a broad umbilicus displaying the edges of all the whorls. Aper- 
ture nearly circular, extensively modified by the penultimate whorl ; 
lip white, thickened and slightly reflected, retreating as it joins the 
